This invention relates generally to optical networks that convey optical signals.
Optical networks may use wavelength division multiplexing so that a plurality of channels, each of a different wavelength, may be multiplexed over the same cable. At a desired termination point for any one of the multiplexed channels, an optical add/drop multiplexer allows light of a given wavelength to be extracted from a plurality of multiplexed light channels. Similarly, a light channel of a given wavelength may be added to the network by an add/drop multiplexer.
One technique for forming an optical add/drop multiplexer is to use the Mach-Zehnder configuration. The Mach-Zehnder interferometer may include two spaced arms, at least one of which may be tuned using a heater. A Mach-Zehnder interferometer may be tuned by changing the refractive index of one of the two arms of the Mach-Zehnder interferometer by heating one arm using an electrical heater.
However, existing heaters have relatively large power consumption when used for purposes of tuning a Mach-Zehnder interferometer. These devices may also exhibit relatively high polarization-dependent losses.
Polarization-dependent losses are losses incurred by various network optical components that are contingent upon the state of polarization of the light interacting with those components. A network component may attenuate light selectively, depending on its state of polarization, changing the intensity of the propagating signal in a random fashion.
Examples of thermal optical devices that exhibit polarization-dependent losses include optical switches, splitters, and variable optical attenuators. A variable optical attenuator is a device that changes the applied attenuation to compensate for example, for the aging of a transmitter or amplifier or to respond to a network's operating conditions. A splitter is a device that splits light into different channels. Optical switches route an optical signal without electro-optical or optoelectrical conversions. Thermal optical devices generally require the application of external power.
Thus, there is a need for better ways to heat thermal optical devices.